Temperature dependence of the 4f quadrupole moment of Yb in YbCu2Si

Abstract

An explanation is provided for the M\"ossbauer measurements on Yb${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$ by which the temperature-dependent quadrupole moment $Q(T)$ of Yb is obtained. The quadruple splitting of the $^{174}\mathrm{Yb}$ M\"ossbauer line is a direct probe of the noncubic crystalline electric field. We compute $Q(T)$ by using the noncrossing approximation to a Green's-function formulation of the Anderson impurity problem. The observed $Q(T)$ behavior is well reproduced by our theory. The zero-temperature value $Q(0)$ is discussed within the frame of the variational ground state proposed by Varma and Yafet and by Gunnarsson and Sch\"onhammer.